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Tracking shows ocean trash doesn't stay put

Far from staying in giant oceanic garbage patches, ocean trash moves around much more than we previously thought, which is bad news for marine life. James Mitchell Crow reports.

The world’s oceans hide a dirty secret. Each harbours a great garbage patch, a vast area in which all the plastic that ends in the ocean gathers, due to the action of wind and currents.

As unappealing as these places sound, the plastic there is relatively harmless to ocean ecology; the patches form in nutrient-poor ocean waters where little life. However, UNSW oceanographer Erik Van Sebille has discovered garbage does not necessarily stay there forever.

Van Sebille made his discovery while attempting to trace the source of all the ocean’s plastic garbage. For the past three decades, ocean researchers have been launching “global drifter buoys”, beach ball-sized devices that ride ocean currents and report their position back to a satellite every six hours. “They are like garbage that phones home,” Van Sebille says.

Using this data, Van Sebille found that eddies in ocean currents could suck garbage back out of the great patches. From there, the rubbish could eventually travel anywhere in the world, he says. So although plastic washed into the ocean from a Sydney beach would first travel to the South Pacific garbage patch, it could end up in any patch, he says.

The porous nature of the patches makes it even harder than previously thought to identify the sources of ocean garbage. It also makes the plastic’s environmental impact much more significant. Each piece of plastic can travel through ecologically sensitive coastal areas multiple times as it travels from patch to patch.

“We know that some birds are heavily affected – albatrosses in the Pacific have stomachs full of plastic bottle caps and small plastic pellets,” Van Sebille says. He is currently working with ecologists to overlay the movements of ocean garbage with the routes of migratory seabirds, to identify the areas where the plastic’s impact is the greatest. www.adrift.org.au